The present invention relates to gas turbine engines, and, more specifically, to turbine airfoils.
In the manufacture of turbine airfoils, it is often necessary to drill cooling holes through the outer airfoil walls entering the internal air passages. These holes provide a source of cooling air to the airfoil surface during engine operation. Several techniques, such as laser beam drilling, electro-discharge machining, or electro-steam drilling, are used to drill turbine airfoil cooling holes. After the drilling process, the cooling holes must be inspected to determine if they are open to the internal cavities. Methods used to inspect for holes that are not properly drilled through or are plugged include pin-check, by inserting a pin wire into the cooling holes; waterflow inspection; and black light inspection using a beam blocking wax and a fluorescent penetrant mixture.
With the incorporation of laser drill methods that do not require the use of beam blocking wax, manufacturing has become more limited by manual pin-check. Manual insertion of pin wires into 100% of the cooling holes on 100% of all parts processed by laser drilling not only adds cost to the manufacturing process due to the time needed to perform this task, but the pin-check method also presents ergonomic concerns due to repetitive hand motion.
It would be desirable, therefore, to provide an inspection technique that overcomes some of the manufacturing and other limitations of existing cooling hole inspection methods.